The invention relates to a device for producing oxygen by means of a chemical reaction, according to the preamble of claim 1.
Aircraft in civil aviation as well as in the military field are usually equipped with an emergency system for the supply of oxygen during a pressure drop in the cabin.
A pressure which, compared to the pressure on the ground, is reduced by roughly a quarter prevails in the aircraft cabin, i.e. the cabin pressure is artificially held at three-quarters of the atmospheric pressure at sea level, i.e. approx 750 hPa, during the cruising phase, i.e. the phase between take-off and landing and in which the aircraft has reached its cruising altitude of about 10000 m. However, a pressure of roughly a quarter of the inner pressure of the cabin prevails outside the aircraft at an altitude of 10000 m. A pressure drop in the cabin of the aircraft can occur if the pressure in the cabin suddenly drops, for example due to a defect in the outer skin of the aircraft. Oxygen masks fall from the panelling above the seats, in order to supply passengers with sufficient oxygen in such situations. These oxygen masks are usually supplied with chemically produced oxygen. For this, chemical oxygen generators are provided above the seats, in which generators a continuous chemical reaction takes place, triggered by a thermal ignition, e.g. by a pull on the oxygen mask, by way of which reaction oxygen is produced and is released to the masks in a defined manner.
A device for producing oxygen by way of a thermal decomposition of a chemical located in a cartridge housing is known for example from DE 44 37 895 C1. There, departing from an activation location, oxygen is produced in a more or less uniform manner along a reaction front propagating in the interior of the cartridge housing in the direction of an unconsumed chemical, until the chemical located in the cartridge is consumed.
If an emergency situation as is described above occurs, a descent is immediately initiated by the pilots, in order to reach an altitude, at which pressure conditions permitting a normal breathing without additional supply of oxygen again prevail. An increased oxygen demand therefore exists in the first minutes in particular during the descent phase, whereas only a reduced oxygen supply is necessary with the continued flight at the reduced altitude (holding altitude) which is subsequent to the descent.
In the state of the art, it is known on the one hand to additionally provide a flow controller, in order to provide a [closed-loop] control of the oxygen supply, wherein this is quite expensive. On the other hand, it is also known from the state of the art, to achieve a changing oxygen production rate and thus supply rate by way of adapting the cross section of the chemical core, in which the reaction takes place. This for example can be effected by way of the thickness of the core being designed in a manner increasing or decreasing over the length, over which the reaction front propagates. However, with these solutions known from the state of the art, there is the disadvantage that the core must have a non-uniform geometry, which can compromise the mechanical stability of such a device producing oxygen.
From US 2004/0151639 A1 and U.S. Pat. No. 7,494,624 B2, it is counted as belonging to the state of the art, with a chemical oxygen generator, not to provide the activation location at the end of the chemical core, but on its side or middle, so that the reaction front propagates in different, in particular opposite directions, by which means the oxygen is produced in a shorter time than is the case with reaction cores ignited at one side.